DESCRIPTION: During the initial two funding periods, the investigators have determined that specific gangliosides (GM-1) inhibit ligand induced dimerization and tyrosine phosphorylation of PDGFR. Results of these studies clearly demonstrated that gangliosides play a regulatory role in several platelet derived growth factor (PDGF)-mediated events involved in cell growth. The investigators believe that they have uncovered an important previously unrecognized regulatory mechanism through which glycoconjugates can modulate and coordinate entire signal transduction pathways by regulating the receptor dimerization (activation of dimerizable receptors). The investigators further proposed to continue the study to define critical gangliosides-PDGF receptor interactions. The investigators hypothesized that there is a specific ganglioside binding domain on the PDGFR through which gangliosides regulate PDGFR dimerization and function. They will test this hypothesis for GM-1, a ganglioside found to have pronounced inhibitory effects on the PDGFR. The investigators propose to continue their studies for further understanding which will be answered by the results obtained from three general specific aims. Aim 1 is to transfect PDGFR in cell lines and characterize several receptor and post receptor functions. Furthermore, they will use GM-1 to inhibit such functions. In Specific Aim 2, they propose to locate the GM-1 binding domain in PDGFR by gene deletion experiments. Subsequently, they propose to mutate this specific domain and identify specific amino acids necessary for GM-1 binding. In Specific Aim 3, they propose to characterize several receptor functions and preceptor events in U251MG and Sf9 cells transfected with GM-1 binding negative mutants identified in Specific Aim 2. The investigator believes that the results of these experiments will test their hypothesis and allow them to define the polypeptide sequence of GM-1 binding domains in the PDGFR through which GM-1 can regulate PDGFR function.